California Gov. Jerry Brown warned that President Trump has just made a “colossal mistake” in gutting the federal government’s effort to combat climate change, which will ignite a response Trump is unprepared to handle.

“It defies science itself,” Brown said in a call to The Times shortly after Trump signed an executive order that aims to bring an abrupt halt to the United States’ leadership on global warming. “Erasing climate change may take place in Donald Trump’s mind, but nowhere else.

“Yes, there is going to be a countermovement,” Brown vowed, predicting Trump’s actions will mobilize environmentalists in a way President Obama never could. “I have met with many heads of state, ambassadors. This is a growing movement. President Trump’s outrageous move will galvanize the contrary force. Things have been a bit tepid [in climate activism]. But this conflict, this sharpening of the contradiction, will energize those who believe climate change is an existential threat.”

Brown and other big-state governors and mayors are moving swiftly to fill the global leadership vacuum Trump created with Tuesday’s directive, which stops short of officially pulling the U.S. out of the Paris climate accord of 2015.

“I see Washington declining in influence, but the momentum being maintained by California and other states aligned with China and those who are willing to do something,” said Brown, who will be traveling to China soon for meetings on climate. “There is a growing activism on the part of millions of people who will not stand by and let Donald Trump effectively tear up the Paris agreement and destroy America’s climate leadership and jeopardize the health and well-being of so many people.”

In the face of Trump’s retreat on climate change, Brown said California will step up its own efforts to push others toward clean energy. “We are not fully meeting the challenge of climate change yet,” he said. “We are doubling down on our commitment. We are reaching out to other states in America and throughout the world and other countries. … We have plenty of fuel to build this movement.

“This is real,” Brown said of the threat created by climate change. “The nations of the world have recognized it in Paris. … I will continue doing my best to work with and rouse the world community, whatever the politicians in Washington do or don’t do.”